I've just tested this on our Windows system with 9.0.4 Lite and it's working OK here. The required CODECs are installed from the Resolve installation. I wonder if installing Avid Codecs separately might be the issue?

Can you try a test of rendering a Quicktime DNxHD 1080p 444 file from Resolve and see if that works? And if it does, can you load that file into Resolve? If so, the files you have may be something Resolve does not support. And if that turns out to be the case, can you send us a sample file to examine?